Removal of iron scale deposits from water sources is a problem for residential households, apartment complexes and commercial office buildings. In heavily urban areas, this problem is often magnified due to the age of the buildings and the inaccessibility to the water pipes for routine maintenance.
Conventionally, drinking water for city buildings may be supplied to each floor from a tank installed on the buildings roof. The water is pumped up from underground storage tanks to a rooftop tank. Over a period of time, iron rust scale and deposits accumulate within the pipes as they pipes age and deteriorate. Dissolved minerals within the water also contribute to scaling and the accumulation of deposits. Further, during warm weather months the pipes may be subject to algae blooms within the water. Even if water for a building is supplied from municipal sources rather than a storage tank, the age of the existing pipes may contribute to scale deposits within the water supplied to the consumer. All of these factors combine to reduce the quality and potability of the water.
Prior art attempts at remedying the problem of scale deposits have historically focused upon the development of methods for chemically treating the water within the pipes. However such attempts have often been met with limited success.
U.S. Pat. No. 4,610,728 (Natesh et al.) discloses a process for dissolving deposits of magnetite from a metal surface by contacting the surface with an aqueous solution of an alkali metal borohydride and an iron chelating agent. U.S. Pat. No. 4,828,743 (Rahfield et al.) discloses a method for removing rust stains from a solid surface by applying oxalic acid based upon the total composition of ferrous iron and mineral acids. The process also includes a rinsing step. U.S. Pat. No. 4,108,680 (Barr, Jr.) discloses a process for the removal of calcium oxalate scale from a metal surface by contacting the scale with an aqueous suspension of nitric acid and manganese dioxide. Finally, U.S. Pat. No. 2,631,950 (Rosenfeld et al.) discloses a method and composition for removing rust and scale from engine cooling systems by supplying a solution containing an oxalic acid and a hydrolyzable chloride of a trivalent metal. The solution is then contacted with the surface of the metal at elevated temperatures.
All of the above noted prior art rust removal methods suffer from a general disadvantage in that they are all inherently short term solutions. Further, they require a variety of steps and chemicals which must be applied sequentially. Very often these numerous chemicals inhibit the chlorine-based disinfecting chemicals which are already in the water. In addition, all of the prior art scale removal methods are either expensive and/or time consuming in application.
Because of the contamination risk from bacteria and water born algae, water sources within urban areas are often treated with chemicals to "activate" the water thereby reducing the risk of contamination as well as undesirable odors and coloration. Conventionally speaking, city water will contain between 0.1 to 2.1 mg/l of chlorine as a disinfectant. Once chlorine contacts the water it generates both hypochlorous acid and hydrochloric acid as indicated in reaction (I) given below: EQU Cl.sub.2 +H.sub.2 O.fwdarw.HCl+HCLO (I)
Although the above reaction occurs rapidly, it does not easily proceed to completion and generally reaches an equilibrium after generating about 50% of the hypochlorous acid at a pH value between about 7 and 8. This inability to generate hypochlorous acid to completion is often due to the high solubility of chlorine. At 25.degree. C., chlorine has a solubility of 0.67 g/100 cc. The hypochloric acid produced in the chlorination reaction of water given in reaction (I) also serves to generate additional disinfecting compounds such as dichlorine oxide and chlorine dioxide and as indicated in reaction (II) and (III) give below: EQU 2 HClO.THETA.Cl.sub.2 O+H.sub.2 O (II) EQU 4 HClO+Cl.sub.2 .rarw.4 HCl+2 ClO.sub.2 (III)
All three reactions serve to disinfect and deodorize water within a particular water source and collectively activate the water.
Prior art rust and scale removal processes often inhibit or deteriorate the disinfecting characteristics of activated water. Further, the prior art iron scale removal processes are not suitable for treatment with plumbing associated with drinking water since a number of the prior art chemicals are potentially toxic at elevated levels. Hence, prior art scale removal processes fail to provide a practical means for removing rust buildup and maintaining a rust-free environment within the pipes once treatment has occurred.